Production of cuprous oxide, a solar cell material, by thermal oxidation and a study of its physical and electrical properties

Cuprous oxide (Cu2O) is a non stoichiometric defect semiconductor. It is envisaged that this semiconductor could be utilised for the fabrication of low-cost solar cells. Copper foil samples, were oxidised in air between 200 degrees C and 1050 degrees C. The oxide films grown were then investigated by means of both XRD and SEM. The electrical characteristics of Cu2O films were analysed by means of the hot-probe thermoelectric method, resistivity and mobility measurements. Oxide films formed between 1040 degrees C and 1050 degrees C were observed to consist entirely of Cu2O and showed p-type semiconductivity while those grown between 200 degrees C and 970 degrees C consists of a mixture of cupric oxide (CuO) and Cu2O. The CuO layer formed was found to be also p-type semiconducting. Thermodynamic calculations indicate that CuO in the mixed oxide layer could be explained in terms of the oxidation of Cu2O. Cu2O layers grown in air without the annealing process gave resistivities in the range 2 x 10(3)-3 x 10(3) Omega cm. A substantial reduction in the resistivity of the samples was achieved by doping with chlorine during growth and annealing. An average mobility of 75 cm(2) V-1 s(-1), at room temperature, was obtained for eight unannealed Cu2O samples. This average value increased to 130 cm(2) V-1 s(-1), after doping the samples with chlorine and annealing. (C) 1998 Elsevier Science B.V. All rights reserved.